Production of light.



S. O. HOFFMAN. PRODUCTION 0F IzIYGYHTL`-` AEPLIGATION FILED JULY 17, 19`T.

Patented Oct. 29, 1912.

2 SHEETS-SHEET 1.

s. o. HOFFMAN.

PRODUCTION OF LIGHT.

APPLIGATION FILED JULY17. 1911.

1,043,008. Patented 001211912.

2 SHEET S-BHEET 2.

`larged scale.

SAMUEL o. IIoiiriiiAN,y or sAN FRANCISCO, CALIFORNIA PRODUCTION OF LIGHT.`

Speci'cation of Letters Patent.`

Patented Oct. 29, 1912.

`Appumun nica my 17, 1011,.` ,serial No. 638,911.

To all whom 'it may concern:

Beit known that I, vSAMUEL O. HOFFMAN, citizen of the United States, residing in the city and countyof San Francisco and State oCalifornia, have invented new and useful Improvements in Production of Light, of which the following is a' specification.V

This invention comprises a method for the production of light from an incandescent body, without the production of waste-l ful heat, and more generally, of producing radiation of particular wavelengths from a source emittingA wavesof the desired and otherwave lengths, with a consumption of energy equivalent to the desired radiation only, and .not to the total radiation of the The drawings illustrate suitable means for ract-ising the invention; Figure 1 being a si e elevation in partial section of a complete lamp embracing the invention. Fig. -2 is a transverse section of a portion of the inner bulb lof Fig. 1 drawn on a greatly en- Fig. 3 is a modification, showing a simple form of the invention in which a film. ofsilver is applied to the inner surface of a lamp bulb.

Light consists of waves in the ether" of certain lengths, capable of aifecting the retina. Waves o greater length, called infra-red `waves are non-luminous. Both the luminous and infra-,red waves upon absorption by a body are converted into heat.

Aside from their physiological ,.eiects, the

'candescent bodies.

only difference between the luminous and infra-red waves is the longer wave length of the latter. i

Practically all yofthe present systems of lighting Vdepend u'ponthe radiation of inbody consists of waves of all lengths, only a small portion of which areluminous, most of the energy. being in the `longer nonluminous infra-red waves. The wave length carrying the maximum energy decreases as the temperature is raised, according to the and the higher the temperature the larger the .proportion of luminous radiation present. `At the highest possible o erating temperature, only about 1%.,5 oi) the radiation is of `useful wavelengthtluminous) the balance bein infrared waves and non-luminous, so-cal ed heat waves. Thus atleast 95% of the energy I parent that no ener The radiation of such a i used toy keepthe body incandescent is radiated as long non-luminous waves (heat) and so Wasted.v i

My invention consists.. simply in' separat ing the radiation of the incandescent body into the luminous and non-luminous por tions, the small luminous percentage being allowed to :radiate `freely, whileI the nonluminous waves, representing m'ost of the energy, are directed back tothe incandescent body and used regeneratively, none being allowed to escape. Thus there is no lossof heat, except that representing the small pro# portion of luminous `radiation produced, and the energy required to keep the body at the necessary temperature is .equivalent to' thelight produced, and not to the total radiationat that temperature,"resulting in an enormous increase in efficiency..

Of course the simplest way of accom-k plishing this is to use` a substance which transmits the luminous waves and `reflects the non-luminous. I have vfound that a film of metallic. silver, thin lenough to be transparent, reflects `a large proportion-ofthe infra-red` waves, Fig. 3` shows a lamp making use yof this fact.' VA filament C is placed asnearly. as ossible along the axis of the cylindrical `tu e A, on the inside of 4which deposited a thin film of .silyen The lamp is otherwise similar'to'rthlordi? nary incandescent electric lamp. rIfh'e' combined radiation from the `*filament strikes theinnermetallic film normally, the infrared waves arereected back tothe filament,

while the light passes through. Itfis apcanescape ex'ceptin the form of light, an therefore, no wasteful v heatv is produced.

While I have only shown two methods of practising my invention. it is possible to make use of any means whatsoever by which the'luminous wavesican be separated from the non-luminous; the essence of my invention being the fact that vthe non-luminous radiation is directedback to the source' without loss and :used regeneratively. For in- -stance with respect 'to the first method described, 'there are a large numberof substances known to physicists .which have the property` of selective reflection. v I have mentioned silver simply because `I haveac- -tually and successfully tried it.

Another method of producing the inventure of the medium. For any givenme `:dium and WaveI length, the ratio of the sines tion is as follows: AInsteadfof the film of silver, a glass bulb .B shown in section in Fig. 2, is placed :inside the tube A. This bulb has prismatic surfaces formed upon it,

, the effect of which is to transmit the light and reiect the infra-red waves. lThis bulb is ,made as thin as practicable, to prevent loss [by absorption.. Its 'action depends upon the following principles: A radiantbeam pass.

ing obliquely vfrom one medium to another is bent or refracted, to or lfrom the normal to lthe oblique surface, 'depending upon whether the beam is entering a denser or rarer mejdium.v The amount of refraction varies with the wave-length o'f the incident radiation,

with the angle of incidence and with the naof. the angles of incidence and refraction is a constant, known as the refractive index.

For the same medium, the refractive indexvaries'with the wave length of the incident radiation, being greater for luminous than infra-red waves,-etc. If a. radiant beam endeavors to pass from a dense to a rarer medium, at an angle to the normal greater than a certain critical angle, it will not suclceed in passing out, but will be totally reflected; in fact this arrangement makes the most perfect reflector known. Now this critical angle of total reflection is equal to .the angle whose sine is'the reciprocal of the refractive index, and therefore, is less for waves of short than of long length and less for luminous-than for infra-red waves. In

aparticular glass that I experimented with, the refractive index for red light, the light of longest wave length, was 1.528, andfor the maximum infrared 1.496. Therefore the critical angle forl red light (sine of critical angle reciprocal .of refractive index) is 40 53', and for the maximum infrared wave length about 43. It is apparent therefore, that if a beam 4containing luminous and infra-red waves should seek to leave the glass at an angle'to the normal of about necessaryangl'es would' depend upon the re- 'fractive 'index of.' thejp'articular glass v4used,

in this cas'ethe vlaluesare those given 'in the preceding paragraphJfA radiant beam K from the filament containing luminous and f for-the luminous waves, they willbe totally reflctedlong the path M P, again refiected Y at an infra-red waves 'enters the glass normally Tand' strikes the surface- M at an angle of 41; as this yis greater than the critical angle l finally passing out normally 'H, but the angle 41, is less than the critical angle for the infra-red Waves, therefore, they will pass out, being refracted along M O, striking the surface O of the ri ht angle prism at an angle of 45, and being reflected along O R, again reflected at R, along VIt S, entering the glass at S and passing out normally, T, thence back to the lilament. Itis `thus seen that no radiant energy can escape from the filament except in the form of luminous Waves, the infra-red waves, which carrymore than 95% of the energy being continually reflected back, and used regeneratively In the arrangement shown for practical reasons, there will be a small waste space as at E To prevent loss,

this space is closed with right angle risms which reiect back both light and in ra-red radiation, as the beam Y, W, X, Z.

If the surface M were so constructed that the beam should strike Vit at say 419,9, a large portion of the red rays would be ref llected back along with the infra-red and thus a source (filament) giving out a light rich in red, could be made to give a pure white light. This also is of importance, as allowing incandescent lamps to be run below voltage, this giving a very long life. While the lamp I have illustrated .is an incandescent electric lamp, it is of course a simple matter to adapt the principle of the invention to any lamp using an incandescent body or bodies. In 4regard to the modification shown in Fig. 2 one mode of forming the bulb is to make it in two concentric pieces, one fitting snugly over the other, as shown, the line of' cleavage C intersecting the inclosed spaces and the prisms X and W being separately inserted before the two parts of the bulb are put together.

The word regenerative -in this application and in the claims, is employed in the sense of being used again or repeatedly without appreciable or apparent loss. The term selective reiector used in this application and in the claims, means any sort of a refiector or refiecting surface or .object which has the capacity of separating the 'luminous radiation from the non-luminous,

allowing one class of radiation to radiate and reflecting the radiation of the other class to a sourceof radiation:

Having thus described my invention, what, I' claim and desire to secure by Let-ters Patent isf 1. A method of producing light from an incandescent source, which conslsts in separating-the lluminous radiation from the infra-red radiation, allowing the luminous radiation to radiate freely and directing the infra-red radiation backto the source.

2. A method of producing light from an incandescent body or source, which consists in separating the luminous waves from the 1,011.3,ocsv

non-luminous, allowing the luminous waves to radiate freely and using the non-luminous waves regeneratively. v

3. A method of producinglight from an incandescent source, which consists in selecting the luminous radiation and directing the non-luminous radiation back to the incandescent source.

4. A method of producing light from an incandescent source, which consists in selecting the luminous radiation, directingthe non-luminous radiation backl to the incandescent source, and allowing the luminous to radiate freely.-

5. The method-of producing light, which consists in separating part of the luminous radiation reflecting the" non-luminous radiation together with a certain amount of red rays back to the incandescentsource and -trans-- muting the same to produce a white light.

6. The method of producing radiation of desired wave length from a source emitting waves of various lengths, which consists in selecting the desired radiation and directing the remainder of the .radiation back to the v source and using it regeneratively.

7. The method of producing radiation of desired wave length from a source emitting Waves of 'various wave lengths, which consists in the use of a selective reector which selects radiation ofthe desired wave length and directs the radiation of other wave lengths back to the source.

- 8. A methodof producin radiation from an incandescent source, w ich consistsin separating the radiation of luminous character from the radiation of non-luminous character, allowing Vthe radiation of one character toradiatel freely, and directing the radiation of the other character back to the source.

9. The method of producing luminous radiation from an incandescent source,

which consists in allowing the luminous radiation to radiate freely and concentrating and converting the non-luminous radiation into luminous 'radiation b raising the temperature of a radiantA bo y, said converted radiation being allowed to radiate freely.

10. an incandescent source, which consists in separating the radiation Iof luminous .charfrom an incandescentsource and A method of producing radiation from acter from the radiation of non-luminous character, allowing the radiation of one character to radiate freely, and using the radiation of the other character regeneratively.

11. The method radiation from an incandescent source,

which consists in allowing the luminous radiation vto radiate freely for illuminating pur oses and converting the non-luminous radlation into luminous radiation through the medium of a selective reiector and an incandescent source, said converted radia tion being allowed to radiate freely.

12; The method of producing luminous radiation from an incandescent source, which consists in separating the luminous radiation from the non-luminousradiation, allowi of producing luminous l ing the luminous radiation to radiate freely and in concentrating and converting thenon-luminous radiation into luminous radiation by raising the temperature of a, radiant body, said converted radiationbeing allowed to radiate freely.

13. Themethod of .producing luminous radiationfrom an incandescent source, which consists in separatin the luminous radiation from the non-luminous radiation by selective reflection, allowing the luminous radiation to radiate freely and returning the non-luminous rays to the initial incandescent source, thereby converting the nonluminous radiation into 4luminous radiation, said converted radiation being allowed to radiate freely.

14. The method of producing radiation of SAMUEL O. HOFFMAN.

Witnesses:

JAMES MASON,

J oHN H. HERRING.

`desiredwave length from an incandescent y :10o In testlmony whereof I have hereunto 

